[5.8] Return fake objects from facades

[BertvanHoekelen]

For consistency in facade fakes I have added the fakes a return type. That way I can create a property for the fake in the test's setUp method.

Current

public function setUp()
{
    parent::setUp();

    Bus::fake();
    $this->eventBus = $this->app->make(Dispatcher::class);
}

New

public function setUp()
{
    parent::setUp();

    $this->eventBus = Bus::fake();
}

[taylorotwell]

All return doc blocks should be fully qualified to match the rest of the framework.